Revised age for Midway volcano, Hawaiian volcanic chain
New conventional K-Ar, 40 Ar/ 39 Ar, and petrochemical data on alkalic basalt pebbles from the basalt conglomerate overlying tholeiitic flows in the Midway drill hole show that Midway evolved past the tholeiitic shield-building stage and erupted lavas of the alkalic suite 27.0 ± 0.6m.y. ago. The data also show that previously published conventional K-Ar ages on altered samples of tholeiite are too young by about 9 m.y. These results remove a significant anomaly in the age-distance relationships of the Hawaiian chain and obviate the need for large changes in either the rate of rotation of the Pacific plate about the Hawaiian pole or the motion of the plate relative to the Hawaiian hot spot since the time of formation of the Hawaiian-Emperor bend. All of the age data along the Hawaiian chain are now reasonably consistent with an average rate of volcanic propagation of 8.0 cm/yr and with 0.83°/m.y. of angular rotation about the Hawaiian pole.